Automotive vehicles are commonly equipped with audio radios that receive and process signals relating to amplitude modulation/frequency modulation (AM/FM) antennas, satellite digital audio radio systems (SDARS) antennas, global positioning system (GPS) antennas, digital audio broadcast (DAB) antennas, dual-band personal communication systems digital/analog mobile phone service (PCS/AMPS) antennas, Remote Keyless Entry (RKE), Tire Pressure Monitoring System (TPM) antennas, and other wireless systems.
SDARS, for example, offer digital radio service covering a large geographic area, such as North America. Satellite-based digital audio radio services generally employ either geo-stationary orbit satellites or highly elliptical orbit satellites that receive uplinked programming, which, in turn, is rebroadcasted directly to digital radios in vehicles on the ground that subscribe to the service. SDARS also use terrestrial repeater networks via ground-based towers using different modulation and transmission techniques in urban areas to supplement the availability of satellite broadcasting service by terrestrially broadcasting the same information. The reception of signals from ground-based broadcast stations is termed as terrestrial coverage. Hence, an SDARS antenna is required to have satellite and terrestrial coverage with reception quality determined by the service providers, and each vehicle subscribing to the digital service generally includes a digital radio having a receiver and one or more antennas for receiving the digital broadcast.
GPS antennas have a broad hemispherical coverage with a maximum antenna gain at the zenith (i.e. hemispherical coverage includes signals from 0° elevation at the earth's surface to signals from 90° elevation up at the sky). Emergency systems that utilize GPS, such as OnStar™, tend to have more stringent antenna specifications. For example, GPS antennas for emergency systems are usually located on large ground planes to improve signal reception performance. In the case of GPS antennas mounted on vehicles, the rooftop of the vehicle becomes the ground plane that provides improved antenna performance, and therefore, is the best receiving location.
However, unlike GPS antennas which track multiple satellites at a given time, SDARS antennas are operated at higher frequency bands and presently track only two satellites at a time. Thus, the mounting location for SDARS antennas make antenna reception a sensitive issue with respect to the position of the antenna on the vehicle. As a result, SDARS antennas are typically mounted exterior to the vehicle, usually on the roof of the vehicle, which presents major difficulties for vehicle manufacturers, causing design changes in the vehicle manufacturing process.
A number of other antenna systems have also been proposed that provide for the reception of radio frequency (RF) signals on vehicles, V. FIG. 1 illustrates a known antenna system, which is seen generally at 1, that allows transfer of RF energy across a dielectric, such as glass, for reception of any desirable wireless signal, such as AM/FM, SDARS, GPS, DAB, or PCS/AMPS signals. The antenna system I is an externally-mounted system and obviates the undesirable practice of having to drill installation holes through the windshield or window of an automotive vehicle, V. Typically, when such installation holes are drilled, a proper seal would have to be provided to protect the interior of the vehicle, V, and its occupants from exposure to external weather conditions. Although not illustrated, it is known to mount SDARS antennas on the trunk or rear fender portion of the vehicle as well via the installation hole process or through other magnetically coupling means. The installation of such antennas is difficult for high volume vehicle producers, as special vehicle roofs and installation processes have to be employed. Without disturbing the vehicle roof structure, antennas can be mounted magnetically on the roof, but the cables coming out of the antenna unit have to enter the vehicle's interior through a windshield-roof gasket, backlite-roof gasket, or some other passage.
To avoid mounting antenna systems on the vehicle's exterior, the antennas can also be mounted inside the instrument panel (IP) of the vehicle. Although IP-mount antennas suffer considerable performance degradation (e.g. as a result of surrounding medium interference, such as structural cross-car beams and other electronics, and overhead interference from the roof) compared to rooftop-mount configurations, IP-mount antennas are often preferred due to their hidden and aesthetically-pleasing location inside the vehicle. Even further, studies have shown that hidden inside-vehicle-mount SDARS antennas exhibit poor satellite and terrestrial reception qualities. However, although it is known that performance of the antenna suffers, vehicle manufacturers and vehicle owners favor hidden antennas for their ease of installation and aesthetically pleasant appearance, respectively.
Accordingly, it is therefore desirable to provide an improved antenna assembly that has reduced signal interference, improved antenna performance, is aesthetically pleasing, and easy to install.